1. Technical Field
The present invention relates to measurement instruments that determine the quality of a modulated signal from a base station in the presence of distortion. More particularly, the present invention relates to method for a test instrument to determine the quality of a signal transmitted by a base station that uses Code Division Multiple Access (CDMA) based technology in the presence of multi-path and co-channel interference.
2. Related Art
There are several products on the market today designed to measure over-the-air wireless signal quality. These products currently include the Anritsu MT8212B, MT8220A, MT8222A, MS2721B, MS2723B, and MS2724B, all available from Anritsu of Morgan Hill, Calif. Additional products currently available include the Tektronix NetTek Analyzer and the Agilent E7495B. At least some of these wireless measurement instruments provide a standard quality indicator for a modulated signal in terms of error vector magnitude (EVM), or the ratio of the ideal modulated power to the total received power (Rho). However, neither determination of EVM or Rho can determine if distortion comes from the signal transmitter itself or the transmission path.
Hence, to know the true health of a base station transmitter, technicians often have to climb up a tower for a direct cable connection or move around on the ground for a location with minimal over-the-air distortion. The former is inefficient and dangerous, while the latter is dependent on one's experience level and luck.
Thus, it is desirable to provide a method for measuring the quality of a base station transmitter while minimizing the effect of distortion without requiring the technician to move around for a minimal distortion location.